Eu começo a trabalhar às nove em ponto.

In Portuguese (Portugal) the verb começar requires the preposition a before another verb in the infinitive. It’s equivalent to English “begin to.”

• Correct: começar a trabalhar
• Incorrect (in standard EP): começar trabalhar

So whenever you use começar (or its past/future forms), remember the pattern começar a + infinitive.

• às is the contraction of the preposition a (at/to) + the definite article as (the, feminine plural).
• Even though nove looks like a singular number, we always treat horas (hours) as feminine plural when telling time, so it’s like saying a as nove horas → às nove.

In short: às = a + as, because you’re implicitly saying horas.

em ponto means “exactly” or “on the dot.” It emphasizes punctuality.

• With em ponto: Eu começo a trabalhar às nove em ponto. → “I start work at exactly nine o’clock.”
• Without em ponto: Eu começo a trabalhar às nove. → “I start work at nine o’clock.” (you’re still understood, but it’s less forceful about exactness)

No, European Portuguese often drops subject pronouns because the verb ending shows the subject. So you can say:

• (Eu) começo a trabalhar às nove em ponto.
  Both are acceptable, but including eu adds a bit more emphasis on “I.”

Yes. Portuguese is flexible with time phrases. Placing às nove em ponto at the beginning is perfectly natural and even common in speech or writing:

• Às nove em ponto, eu começo a trabalhar.
  This often adds a slight focus on the time itself.

You can ask:

• A que horas começas a trabalhar? (informal/familiar)
• A que horas começa a trabalhar? (formal or when speaking to someone you don’t know well)

Note the same começar a + infinitive pattern and the question form A que horas…?

In Brazilian Portuguese (BP), you still use começar a + infinitive in formal registers, but in casual speech you may hear people drop the a:

• Standard BP/EP: começo a trabalhar
• Colloquial BP: começo trabalhar (though grammatically debatable)

Also, BP speakers might prefer vou começar a trabalhar às nove (“I’m going to start working at nine”) if speaking in near-future contexts.

Yes. Both are correct:

• às nove em ponto
• às nove horas em ponto

Including horas is more formal or precise, but most people simply say às nove.